1. Field of the Invention
The present invention relates generally to medical devices and procedures, and more particularly, relates to medical devices and procedures for removing thrombus deposits from the cardiovascular system.
2. Description of the Prior Art
Procedures and apparatus have been developed for ease in removing tissue and various deposits. U.S. Pat. No. 4,790,813 issued to Kensey and U.S. Pat. No. 4,842,579 issued to Shiber describe techniques for the removal of plaque deposited in arteries by mechanical ablation using rotating cutting surfaces. These relatively traumatic approaches are directed to the treatment and removal of very hard substances.
In current medical procedures, thrombus deposits are often removed using a catheter such as is described in U.S. Pat. No. 4,328,811 issued to Fogarty. In this system, a surgical cutdown is performed to access the vessel and allow catheter entry and advancement to a point beyond the deposit. The balloon is inflated and the catheter is withdrawn pulling the deposit along with it.
Pressurized fluids have also been used in the past to flush undesirable substances from body cavities. U.S. Pat. No. 1,902,418 describes such a system for domesticated animals. The more modern approaches tend to use vacuum rather than gravity as the primary means for removal of the deposits or tissue and relatively low fluid pressures to cut into and fragment the substances to be ablated.
U.S. Pat. No. 3,930,505 issued to Wallach describes a surgical apparatus for the removal of tissue from the eye of a patient. As with similar systems, Wallach uses a relatively low pressure jet of water (i.e. 15 to 3500 psi) to disintegrate the tissue, and a suction pump to perform the actual removal.
A similar approach applied to the cardiovascular system is discussed in U.S. Pat. No. 4,690,672 issued to Veltrup. Veltrup also provides a much lower pressure jet of water (i.e. less than 450 psi) to fragment deposits. As with Wallach, Veltrup uses a vacuum pump for evacuation of the fragments. The distal end of the Veltrup catheter is readily repositionable to permit manual entrapment of the deposits to be fragmented.
The present invention overcomes the disadvantages of the prior art systems by performing the entire procedure at positive pressures. This eliminates the need for a vacuum pump and provides the added safety feature of an intravascular environment which is always positively pressurized as during normal functioning of the cardiovascular system. This tends to prevent collapse of the vessel. The system also controls the exposure of the vessel to over pressurization and prevent distension.
According to the present invention, the only energy added to the system is via an extremely high pressure stream of saline solution. This stream serves to dislodge thrombus deposits, position them, and then emulsify them. Thrombus particles are attracted to the jet due to the localized high velocity and low pressure. Recirculation patterns and fluid entrainment bring the thrombus continually into close proximity of the jet. Once emulsified by the jet, the particles are removed by flow through the evacuation lumen generated as a result of stagnation pressure which is induced at the mouth of the evacuation lumen by the action of at least one fluid jet directed at and impinging on the lumen mouth.
The procedure is practiced by percutaneously or intraoperatively entering the vascular system of the patient at a convenient location with a cannula. The catheter is inserted either directly or over a previously positioned guide wire and advanced under fluoroscopy to the site of the vascular occlusion or obstruction which generally contains an aggregation of blood factors and cells or thrombus deposit, which is normally identified by angiography. One or more balloons may be inflated to stabilize the distal end of the catheter and provide a degree of isolation of the area to be treated.
Sterile saline is pressurized by a disposable pump and directed through a flexible metallic tube within the catheter. One or more jets at the distal end of the catheter direct the pressurized stream generally in the direction of the mouth of the evacuation lumen at the distal end of the catheter with a component directed toward the vessel wall. One function of the jet(s) alone or in combination with a distal balloon, is to dislodge thrombus deposits from attachment to the vessel wall. Other functions of the jet(s) are to attract and emulsify the thrombus deposits and create the stagnation pressure which evacuates the emulsion.
A metering device is utilized at the proximal end of the evacuation lumen to regulate the flow rate of the emulsified thrombus out of the catheter. Because the entire system operates at a positive pressure, the output must be metered to prevent excess evacuation. Safety monitors turn the system off if one of the lumens or jets becomes clogged. An optional monitor at the distal end of the catheter can monitor power delivery and degree of blockage. An alternative embodiment of the invention provides an extra lumen for monitoring of temperature and/or pressure at the site of the thrombectomy. The evacuation lumen permits the passage of an angioplasty dilatation catheter or angioscope for intravascular viewing.